Radiation risks“Acceptable risk” is a better way to think about radiation exposure in Fukushima

Five years after the Fukushima disaster, many of these people remain refugees, unable to return home for fear of radiation exposure. As the radioactivity cleanup continues, people are coming to an uncomfortable realization: although cleanup can reduce the level of radioactive contamination, the environmental radiation dose levels within the prefecture will remain elevated for many generations before they finally reach the very low levels that existed prior to the accident. So, when will it be safe for people to return to their homes and to normal life in the Fukushima Prefecture? With regard to radiation exposure, “safe” really means an “acceptable level of risk,” and not everyone agrees on what is acceptable. Providing people with this risk characterization information, at the very least, is within the power of all radiation regulatory agencies, even if achieving complete cleanup of the environment is beyond their reach. This public information void about radiation risks needs to be filled. People can make their own decisions once they’re empowered with credible and intelligible risk information.

On 11 March 2011, the Fukushima Prefecture of Japan experienced multiple nuclear reactor meltdowns as a consequence of an earthquake and a subsequent tsunami. The meltdowns resulted in the release of radioactivity into the environment and 150,000 people were evacuated from their homes specifically due to radiation concerns.

Now, five years later, many of these people remain refugees, unable to return home for fear of radiation exposure. As the radioactivity cleanup continues, people are coming to an uncomfortable realization: although cleanup can reduce the level of radioactive contamination, the environmental radiation dose levels within the prefecture will remain elevated for many generations before they finally reach the very low levels that existed prior to the accident.

So, when will it be safe for people to return to their homes and to normal life in the Fukushima Prefecture? As I explain in my book, Strange Glow: The Story of Radiation, there may be 150,000 different answers to that question.

“Safe” has a fluid meaningWith regard to radiation exposure, “safe” really means an “acceptable level of risk,” and not everyone agrees on what is acceptable. The Japanese government has set an annual effective dose limit to the public of 20 millisieverts (mSv) per year above background as its remediation goal for the Fukushima Prefecture – up from one mSv per year, which was the official limit for exposures to the public prior to the incident. Although accurate numbers are hard to come by, it’s been estimated that about 50 percent of the original evacuation zone remains restricted because its radiation levels still exceed 20 mSv per year, and for half of this restricted half (about 25 percent of the total evacuated area) annual dose levels still exceed 50 mSv per year.

To the Japanese people, this raising of the annual safety limit from one to 20 mSv appears like the government is backpedaling on its commitment to safety. They suspect it’s because the government knows it is not technically or financially feasible to deliver on any cleanup commitment to reduce the annual effective dose below 20 mSv, and that, of course, is true. This is the problem with moving regulatory dose limits after the fact to accommodate inconvenient circumstances; it breeds distrust.